This invention relates generally to semiconductor devices, and more particularly, to a semiconductor device having a ball grid array and method therefor.
In some semiconductor manufacturing processes, such as for example, xe2x80x9cflip chipxe2x80x9d, bumps are fabricated on pad areas of a semiconductor die in order to interconnect the die to a package or to a substrate. The substrate is used to interface the electrical circuits of the semiconductor die to a printed circuit board. In some instances, the semiconductor die may be attached directly to the printed circuit board.
An integrated circuit manufactured using xe2x80x9cflip chipxe2x80x9d technology may have hundreds of these solder bumps. In solder ball, or solder bump, technology, various techniques may be used to define the area on the pads for receiving the solder balls. One technique provides a solder ball connection area called a soldermask defined (SMD) bonding pad. Another technique provides a solder ball connection area known as a non-soldermask defined (NSMD) bonding pad.
FIG. 1 illustrates a soldermask defined bonding pad in accordance with the prior art. A SMD bonding pad is provided on both a substrate 12 and on a printed circuit board 22. The SMD bonding pad on substrate 12 includes a metal bonding pad 14 formed on substrate 12. Substrate 12 is generally used to interconnect, or interface a semiconductor die (not shown) with printed circuit board 22. A soldermask coating 16 is formed over substrate 12 and covers a portion of bonding pad 14. A portion of the metal bonding pad 14 is left exposed. A solder ball 24 is then attached to bonding pad 14. When connecting substrate 12 to printed circuit board 22, a bonding pad 20 is formed on the surface of printed circuit board 22. A solder mask 18 is formed over the surface of printed circuit board 22 and overlaps a portion of bonding pad 20 to form another SMD bonding pad. The openings in the soldermask coatings 16 and 18 define the area of the bonding pads to which the solder attaches for making electrical contact between the substrate 12 and printed circuit board 22. Also, the soldermask prevents liquid solder from flowing over areas where it is not wanted, such as for example, along a metal trace. In addition, the soldermask functions to shape the solder ball 24 after it is reflowed.
FIG. 2 illustrates a non-soldermask defined bonding pad in accordance with the prior art. An NSMD bonding pad is illustrated on both a substrate 32 and a printed circuit board 42. The NSMD bonding pad on substrate 32 includes a metal bonding pad 34. As described above in connection with FIG. 1, substrate 32 is used to interconnect, or interface a semiconductor die (not shown) with printed circuit board 42. A soldermask coating 36 is formed over substrate 32 and has an opening that does not typically contact or overlap bonding pad 34. A solder ball 44 is attached to bonding pad 34. Likewise, a bonding pad 40 is formed on the surface of printed circuit board 42 where it is intended to connect to bonding pad 34. A solder mask 38 is formed over the surface of printed circuit board 42 and has openings that do not typically cover or overlap any of bonding pad 40. The shape and size of the bonding pads function to determine the shape of the solder ball after solder reflow.
SMD bonding pads are known to provide greater reliability in applications where the printed circuit board is subjected to high bending loads, such as for example, a cellular telephone that includes push buttons on the same printed circuit board as the integrated circuits. However, SMD bonding pads are not known for providing high reliability in those applications that subject the printed circuit board to thermal cycling, such as for example, in an automotive application. In contrast, NSMD bonding pads are known to provide high reliability in extreme temperature applications, but not high reliability when subjected to bending loads.
Therefore, a need exists for a technique to attach a semiconductor device to a printed circuit board that provides improved bending reliability as well as improved reliability when exposed to temperature cycling.